Process for adhering two substrates with a liquid curable composition

ABSTRACT

This invention relates to curing of coatings, sealants and laminates under ambient conditions without effecting the pot life of a curable liquid composition comprising a polyene containing at least two reactive unsaturated carbon to carbon bonds per molecule and a polythiol containing at least two thiol groups per molecule, the total combined functionality of (a) the reactive unsaturated carbon to carbon bonds per molecule in the polyene and (b) the thiol groups per molecule in the polythiol being greater than four which comprises having present at least a minor amount of an iron-containing material either as a portion of the substrate, as a primer coat for the substrate or as a top coat for the curable composition. In the case where oxygen is excluded from the reaction, a minor amount of an oxime ester is added to the system to assure curing to a solidified product.

United States [72] Inventors Clifton L. Kehr Silver Spring; James L. Guthrie, Ashton, both of Md. [21] App]. No. 793,534 [22] Filed Jan. 23, 1969 [45] Patented Oct. 26, 1971 [73] Assignee W. R. Grace & Co.

New York, N.Y.

[54] PROCESS FOR ADHERING TWO SUBSTRATES WITH A LIQUID CURABLE COMPOSITION 2 Claims, No Drawings [52] U.S.Cl 156/310, 156/326, 260/79.5 [51] Int. Cl B32b 27/32 [50] Field of Search 156/310, 308, 326

[56] References Cited UNITED STATES PATENTS 3,063,891 11/1962 Boylan 156/310 Primary Examiner-Reuben Epstein Attorneys-Richard P. Plunkett and Kenneth E. Prince ABSTRACT: This invention relates to curing of coatings, sealants and laminates under ambient conditions without effecting the pot life of a curable liquid composition comprising a polyene containing at least two reactive unsaturated carbon to carbon bonds per molecule and a polythiol containing at least two thiol groups per molecule, the total combined functionality of (a) the reactive unsaturated carbon to carbon bonds per molecule in the polyene and (b) the thiol groups per molecule in the polythiol being greater than four which comprises having present at least a minor amount of an iron-containing material either as a portion of the substrate, as a primer coat for the substrate or as a top coat for the curable composition. In the case where oxygen is excluded from the reaction, a minor amount of an oxime ester is added to the system to assure curing to a solidified product.

PROCESS FOR ADHERING TWO SUBSTRATES WITH A LIQUID CURABLE COMPOSITION Many polymeric products are supplied for use in coatings, sealants or other such applications in a form of a liquid or a paste. These materials are expected to cure to rigid or elastomeric materials by the action of air, moisture, or heat, by evaporation of volatile components, or by the action or irradiation. Many of these materials have the disadvantage that the curing reactions may take place prematurely in the package. Even in well-known two components systems, the mixed material must be used very soon after mixing because of the short pot life of the reactive system.

One object of the instant invention is to produce a curable liquid composition for coatings, sealants, laminates or other such applications which will cure rapidly under ambient conditions. Another object of the instant invention is to produce a liquid curable composition which is uneffected by exposure to the atmosphere. STILL ANOTHER OBJECT OF THE IN- STANT INVENTION IS TO PRODUCE A LIQUID CURA- BLE COMPOSITION WHICH WILL CURE RAPIDLY ON CONTACT WITH A MINOR AMOUNT OF AN IRON-containing material as a substrate, a primer for the substrate or a top coat for the liquid curable composition. T)ESE AND OTHER OBJECTS WILL BECOME APPARENT FROM A READING HEREAFTER. Still another object of the instant invention is to produce a liquid curable composition which will cure rapidly on contact with a minor amount of an ironcontaining material as a substrate, a primer for the substrate or a top coat for the liquid curable composition. These and other objects will become apparent from a reading hereafter.

Summarily, this invention comprises withholding from a packaged curable liquid polyene-polythiol composition, an ironcontaining catalyst therefor and incorporating said catalyst into the system as the substrate to be coated, as a primer for the substrate to be coated or as a top coat for the curable liquid composition. Prime coats are commonly used to promote adhesion, to act as barrier coats or for other purposes, but as far as is known, have not been used as carriers for reactive ingredients intended to cause curing. The present invention teaches the use of an iron-containing catalyst as a reactive prime coat alternatively as a substrate or a reactive top coat, the invention being the presence of the catalyst solely in the substrate, primer or top coat and not in the bulk premixed liquid curable polyene-polythiol composition. In the instances where oxygen is excluded from the reaction, e.g., wherein the iron-containing catalyst is present in the substrate or as a primer for the substrate and the polyene-polythiol composition is applied directly thereon then, it is necessary to add an oxime ester to the polyene-polythiol composition to effect curing to a hardened solidified product.

According to the invention there is provided a process for preparing coatings, sealants, and laminates which harden quickly under ambient conditions comprising the steps of applying an iron-containing catalyst, with or without a solvent or diluent, as desired, as a prime coat on the substrate to be coated, and thereafter applying to said prime coat a liquid composition comprising a polyene containing at least two reactive unsaturated carbon to carbon bonds per molecule and a polythiol containing at least two thiol groups per molecule, the total combined functionality of (a) the reactive unsaturated carbon to carbon bonds per molecule in the polyene and (b) the thiol groups per molecule in the polythiol being greater than four, to form a hardened coating on said substrate. The addition of minor amounts of an oxime ester to the liquid curable polyene-polythiol composition causes curing to a solid, self-supporting cured polythioether even under inert conditions, e.g., in an argon atmosphere.

The amount of iron in the catalyst operable to cause curing of the liquid polyene-polythiol composition is at least 0.0001 percent by weight based on the liquid polyene-polythiol composition when the catalyst is applied as a primer, topcoat or as the substrate, per se. Ordinarily when the iron-containing catalyst is added as a prime coat or top coat, the amount is usually in the range 0.0001-0.01 percent by weight of the polyene-polythiol composition. Where the iron-containing catalyst is the substrate per se, e.g., an iron pipe, any amount of the iron-containing catalyst in excess of 0.0001 percent by weight of the polyene-polythiol composition may be present and the invention is still operable.

Iron-containing materials which are operable in the instant invention as a catalyst are many and varied and include iron as well as iron containing organic and inorganic compounds. Thus for example, operable compounds include, but are not limited to, iron, iron salts such as sulfate, nitrate, ferricyanide, ferrorcyanide, chloride, ammonium sulfate and the like. Organic iron salts are also operable and include, but are not limited to, oxalate, stearate, naphthenate, citrate and iron chelate compounds such as acetylacetonate, benzoylacetophenonate, ferrorcene and the like. Other operable iron compounds include, but are not limited to, iron acetate, iron orthoarsenate, iron orthoarsenite, iron boride, iron hydroxide, iron iodide, iron lactate, iron maleate, iron oleate, iron oxide, iron pyrophosphate, iron metasilicate, iron sulfide, iron sulfite, iron thiocyanate, and the like. The aforesaid list of iron compounds is merely illustrative and by no means exhaustive, suffice it to say that any iron containing material in the operable amount set out herein will cause relatively rapid curing of the polyene-polythiol composition under ambient conditions.

The amount of oxime ester employed is in the range 0.1 to 5 percent by weight based on the liquid polyene-polythiol composition.

Operable oxime esters which can be added to the liquid polyene-polythiol composition of theinstant invention and cause curing in the presence of the iron-containing catalyst under inert conditions are many and varied. Examples of operable oxime esters include, but are not limited to, dimethylglyoxime dibenzoate, quinone dioxime dimethoxybenzoate, quinone dioxime dichlorobenzoate, diphenylglyoxime dibenzoate, glyoxime dibenzoate, quinone dioxime diacetate, terephthalaldehyde dioxime dibenzoate, dimethylglyoxime diacetate, dimethylglyoxime distearate, quinone dioxime dibenzoate, dimethylglyoxime monoacetate, quinone dioxime dibenzenesulfonate, dimethylglyoxime monobenzoate, terephthalaldehyde dioxime monobenzoate, furil dioxime distearate, diphenylglyoxime distearate, dimethylglyoxime adipate, terephthalaldehyde dioxime distearate, 3-phenyl-4,5-dihydro-6-oxo-l ,2-oxazine, cyclohexanone oxime benzoate, 4-benzoylbutyric acid oxime benzoate, quinone dioxime dinitrobenzoate, 2,4-pentanedione dioxime dibenzoate, quinone dioxime distearate, benzoylpropionic acid oxime benzoate, quinone dioxime diheptanoate, cycloheptanone oxime benzoate, Z-methylcyclohexanone oxime benzoate, l-phenyl-l,2-propanedione dioxime distearate, glyoxime distearate, 2,4-pentanedione dioxime distearate, quinone dioxime dibutyrate, benzophenone oxime stearate, benzaldoxime benzoate, benzaldoxime stearate, glyoxime diacetate, levulinic acid oxime benzoate, and the like. Various other oxime esters are obvious to one skilled in the art and are operable herein.

The polythiols and one group of operable polyenes which can be cured rapidly to form coatings, sealants, and laminates are set out in a copending application assigned to the same assignee having Ser. No. 617,801 filed Feb. 23, 1967 and are incorporated herein by reference. That is, one group of polyenes operable in the instant invention are those having a molecular weight in the range 50 to 20,000, a viscosity ranging from 0 to 20 million centipoises at 70 C. of the general formula: [Al- (X wherein X is a member of the group consisting of and R--C C; m is at least 2; R is independently selected from the group consisting of hydrogen, halogen, aryl, substituted aryl, cycloalkyl, substituted cycloalkyl, aralkyl, substituted aralkyl and alkyl and substituted alkyl groups containing 1 to 16 carbon atoms and A is a polyvalent organic moiety wherein x is at least 1,

2.ethylene/propylene/nonconjugated diene terpolymers, such as "Nordel i040" manufactured by duPont which contains pendant reactive double bonds of the formula: -CH CH=CH-Cl-l 3.the following structure which contains terminal reactive" double bonds:

I CHFCHCH;Ofi-CHz$fi-OCH;CH=CH O CH3)! 0 wherex is at least 1, and

4. the following structure which contains near terminal 4O reactive doublebonds .L i cH3(CHg)7-CHCH CH; C 063116 0 1 II x where x is at least 1.

As used herein polyenes and polyynes refer to simple or complex species of alkenes or alkynes having a multiplicity of pendant, terminally or near terminally positioned reactive carbon to carbon unsaturated functional groups per average molecule. For example, a diene is a polyene that has two reactive" carbon to carbon double bonds per average molecule, while a diyne is a polyyne that contains in its structure two "reactive carbon to carbon triple bonds per average molecule. Combinations of "reactive" double bonds and reactive triple bonds within the same molecule are also possible. An example of this is monovinylacetylene, which is a polyeneyne under our definition. For purposes of brevity all these classes of compounds will be referred to hereafter as polyenes.

A second group of polyenes operable in the instant invention includes unsaturated polymers in which the double or tri- 5 ple bonds occur primarily within the main chain of the molecules. Examples include conventional elastomers (derived primarily from standard diene monomers) such as polyisoprene, polybutadiene, styrenebutadiene rubber, isobutylene-isoprene rubber, polychloroprene, styrene-butadieneacrylonitrile rubber and the like; unsaturated polyesters, polyamides, and polyurethanes derived from monomers containing reactive" unsaturation, e.g., adipic acid-butenediol, l,6-hexanediamine-fumaric acid and 2,4-tolylene diisocyanate butenediol condensation polymers and the like.

A few typical examples of polymeric polyenes which contain conjugated reactive double bond groupings such as those described above are poly(ethylene ether) glycol diacrylate having a molecular weight of about 750, poly(tetramethylene ether) glycol dimethacrylate having a molecular weight of about 1175, the triacrylate of the reaction product of trimethylolpropane with 20 moles of ethylene oxide, and the like.

As used herein for determining the position of the reactive functional carbon to carbon unsaturation, the term terminal means that said functional unsaturation is at an end of the main chain in the molecule; whereas by "near terminal is meant that the functional unsaturation is not more than 16 carbon atoms away from an end of the main chain in the molecule. The term pendant" means that the reactive carbon to carbon unsaturation is located terminally or near terminally in a branch of the main chain. For purposes of brevity all of these positions will be referred to generally as terminal" unsaturation.

The liquid polyenes operable in the instant invention contain one or more of the following types of nonaromatic and nonconjugated reactive carbon to carbon unsaturation:

These functional groups as shown in 1-8 supra are situated in a position either which is pendant, terminal or near terminal with respect to the main chain but are free of terminal conjugation. As used herein the phrase free of terminal conjugation means that the terminal reactive" unsaturated groupings may not be linked directly to nonreactive unsaturated species such as and the like so as to form a conjugated system of unsaturated bonds EXEMPLIFIED by the following structure;

On the average the polyenes must contain 2 or more reactive unsaturated carbon to carbon/bonds/molecule and have a viscosity in the range from O to 20 million centipoises at 70 C. Included in the term polyenes" as used herein are those materials which in the presence of an inert solvent, aqueous dispersion or plasticizer fall within the viscosity range set out above 70 C. Operable polyenes in the instant invention have molecular weights in the range 50-20,000, preferably 500 to l0,000.

As used herein the term reactive" unsaturated carbon to carbon groups means groups having the structures as shown in l-8 supra which will react under proper conditions as set forth herein with thiol groups to yield the thioether linkage as contrasted to the term unreactive carbon to carbon unsaturation which means groups when found in aromatic nuclei (cyclic structures exemplified by benzene, pyridine, anthracene, tropolone and the like) which do not under the same conditions react with thiols to give thioether linkages. in the instant invention coating, sealant and laminate products from the reaction of polyenes with polythiols which contain 2 or more thiol groups per average molecule are called polythioether polymers or polythioethers.

As used herein, the term polythiols refers to simple or complex organic compounds having a multiplicity of pendant or terminally positioned -SH functional groups per average molecule. On the average the polythiols must contain 2 or more SH groups/molecule. They usually have a viscosity range of 0 to 20 million centipoises (cps) at 70 C. as measured by a Brookfield Viscometer. Included in the term polythiols as used herein are those materials which in the presence of an inert solvent, aqueous dispersion or plasticizer fall within the viscosity range set out above at 70 C. Operable polythiols in the instant invention usually have molecular weights in the range 50-20,000, preferably 100-10,000.

The polythiols operable in the instant invention can be exemplifled by the general formula: R where n is at least 2 and R is a polyvalent organic moiety free from reactive carbon to carbon unsaturation. Thus R may contain cyclic groupings and minor amounts of hetero atoms such as N, S, P or 0 but primarily contains carbon-hydrogen, carbon-oxygen, or silicone-oxygen containing chain linkages free of any reactive carbon to carbon unsaturation.

One class of polythiols operable with polyenes in the instant invention to obtain essentially odorless polythioether products are esters of thiol-containing acids of the general formula: HS-R COOH where R is an organic moiety containing no reactive carbon to carbon unsaturation with polyhydroxy compounds of the general structure: R, ,(Ol-l), where R is an organic moiety containing no reactive" carbon to carbon unsaturation and n is 2 or greater. These components will react under suitable conditions to give a polythiol having the general structure:

where R, and R are organic moieties containing no reactive" carbon to carbon unsaturation and n is 2 or greater.

Certain polythiols such as the aliphatic monomeric polythiols (ethane dithiol, hexamethylene dithiol, decamethylene dithiol, tolylene 2,4-dithiol, etc. and some polymeric polythiols such as a thiol-terminated ethylcyclohexyl dimercaptan polymer, etc. and similar polythiols which are conveniently and ordinarily synthesized on a commercial basis, although having obnoxious odors, are operable in this invention but many of the end products are not widely accepted from a practical, commercial point of view. Examples of the polythiol compounds preferred for this invention because of their relatively low odor level include but are not limited to esters of thioglycolic acid (HS-CH COOH), a-mercaptopropionic acid (HS-CH(CH )-COOH and ,B-mercaptopropionic acid (HS-Cl-hCi-QCOOH) with polyhydroxy compounds such as glycols, triols, tetraols, pentaols, hexaols, etc. Specific examples of the preferred polythiols include but are not limited to ethylene glycol bis(thioglycolate), ethylene glycol bis(B-mercaptopropionate), trimethylolpropane tris(thioglycolate trimethylolpropane tris( fi-mercaptopropionate), pentaerythritol tetrakis (thioglycolate) and pentaerythritol tetrakis (B-mercaptopropionate), all of which are commercially available. A specific example of a preferred polymeric polythiol is polypropylene ether glycol bisfl-mercaptopropionate) which is prepared from polypropylene ether glycol e.g., Pluracol P2010, Wyandotte Chemical Corp.) and ,B-mercaptopropionic acid by esterification.

The preferred polythiol compounds are characterized by a low level of mercaptanlike odor initially, and after reaction, give essentially odorless polythioether end products which are commercially attractive and practically useful resins or elastomers for both indoor and outdoor application.

As used herein the term liquid curable compositions" means a liquid composition having a viscosity in the range 0 to 20 million centipoises at 70 C. which is solidified by curing on contact with the iron-containing catalyst disclosed herein under ambient conditions.

The term functionality as used herein refers to the average number of ene or thiol groups per molecule in the polyene or polythiol, respectively. For example, a triene is a polyene with an average of three reactive carbon to carbon unsaturated groups per molecule and thus has a functionality (I) of three. A polymeric dithiol is a polythiol with an average of two thiol groups per molecule and thus has a functionality (f) of two.

It is further understood and implied in the above definitions that in these systems, the functionality of the polyene and the polythiol component is commonly expressed in whole numbers although in practice the actual functionality may be fractional. For example, a polyene component having a nominal functionality of 2 (from theoretical considerations alone) may in fact have an effective functionality of somewhat less than 2. In an attempted synthesis of a diene from a glycol in which the reaction proceeds to 100 percent of the theoretical value for complete reaction, the functionality (assuming 100 percent pure starting materials) would be 2.0. If however, the reaction were' carried to only percent of theory for complete reaction, about 10 percent of the molecules present would have only one ene functional group, and there may be a trace of material that would have no ene functional groups at all. Approximately 90 percent of the molecules, however, would have the desired diene structure and the product as a whole then would have an actual functionality of 1.9. Such a product is useful in the instant invention and is referred to herein as having a functionality of 2.

The aforesaid polyenes and polythiols can, if desired, be formed or generated in situ and still be rapidly cured by the process of the instant invention.

To obtain the maximum strength, solvent resistance, creep resistance, heat resistance, and freedom from tackiness the reaction components consisting of the polyenes and polythiols of this invention are formulated in such a manner as to give solid, crosslinked, three dimensional network polythioether polymer systems on curing. in order to achieve such infinite network formation the individual polyenes and polythiols must each have a functionality of at least 2 and the sum of the functionalities of the polyene and polythiol components must always be greater than 4. Blends and mixtures of the polyenes and the polythiols containing said functionality are also operable herein.

The compositions to be cured, i.e., (converted to solid resin or 'elastomeric coatings, sealants or laminates) in accord with the present invention may, if desired, include such additives as antioxidants, dyes, inhibitors, activators, fillers, pigment, antistatic agents, flame-retardant agents, thickeners, thixotropic agents, surface active agents, viscosity modifiers, extending oils, plasticizers, tackifiers and the like within the scope of this invention. Such additives are usually blended with the polyene or polythiol prior to or during the compounding of the polyene and polythiol. Operable fillers include natural and synthetic resins, carbon black, glass fibers, wood flour, clay, silica, alumina, carbonates, oxides, hydroxides, silicates, glass flakes, glass beads, borates, phosphates, diatomaceous earth, talc, kaolin, barium sulfate, calcium sulfate, calcium carbonate, antimony oxide and the like. The aforesaid additives may be present in quantities up to 500 parts or more per 100 parts of the liquid polyene-polythiol composition by weight and preferably 0.005-300 parts on the same basis.

In all the curable liquid systems herein the compositions consist of 2 to 98 parts by weight of a polyene containing at least 2 reactive unsaturated carbon to carbon bonds per molecule, 98 to 2 parts by weight of a polythiol containing at least 2 thiol groups per molecule and when necessary, i.e., under inert conditions, 0.1 to percent by weight of the polyene-polythiol composition of an oxime ester as a synergistic agent for the iron-containing catalyst.

The compounding of the components prior to curing can be carried out in several ways. Since the oxime esters used in this invention do not by themselves under ambient conditions have a catalytic effect on the curing of polyenes with polythiols but only act as a synergistic agent for the iron-containing catalyst and since iron and its compounds used in this invention act as a catalyst by themselves only in the presence of air, all ingredients except the iron-containing catalyst are mixed to give a stable system. The iron-containing catalyst is applied separately as a prime coat to the substrate with or without a diluent or solvent as deemed necessary depending upon the phase of the iron-containing material or as a top coat for the polyene-polythiol composition. Additionally, if the substrate per se contains an iron-containing material, no additional catalyst is necessary and only the addition of an oxime ester to the polyene-polythiol composition is required to effect curing. The iron compound could be deposited as a prime coat in solution or as a dust in a pattern electrostatically or by other methods to cause complete curing or selective curing only in certain regions of a curable polymer. Various other compounding procedures are obvious to one skilled in the art.

The following examples will aid in explaining but expressly not limit the instant invention. Unless otherwise noted, all parts and percentages are by weight.

PREPARATlON OF POLYENE EXAMPLE I To a 2-liter flask equipped with stirrer, thermometer, and gas inlet and outlet was charged 450 g. (0.45 moles) of polytetramethylene ether glycol having a hydroxyl number of 112 and molecular weight of 1,000, along with 900* g. (0.45 moles) of polytetramethylene ether glycol having a hydroxyl number of 56 and a molecular weight of 2,000, both commercially available from Quaker Oats Co. The flask was heated to 110 C. under vacuum and nitrogen and maintained thereat for one hour. The flask was then cooled to approximately 70 C. where at 0.1 g. of dibutyl tin dilaurate was added to the flask. A mixture of 78 g. (0.45 moles) of tolylene diisocyanate and 78 g. (0.92 moles) of allyl isocyanate was thereafter added to the flask dropwise with continuous stirring. The reaction was maintained at 70 C. for one hour after addition of all the reactants. The thus formed allyl terminated polyene will hereinafter be referred to as prepolymer A.

COATING PROCESSES EXAMPLE It A solution of 100 mg. of ferric acetylacetonate in 3 ml. of acetone was poured into an aluminum weighing dish. The acetone was allowed to evaporate, depositing a prime coat of ferric acetylacetonate on the bottom of the dish. A solution was made up from 30 g. of prepolymer A from example i, 5 g. of Benzoflex 988," a commercially available plasticizer from Velsicol Chemical Corp., 2.3 g. of pentaerythritol tetrabis (l3- mercaptopropionate), a commercially available polythiol from Carlisle Chemical Corina rider the trade name "Q-43" and 0.5 g. of cyclohexanone oxime benzoate. The solution was poured into the aluminum weighing dish containing the ferric acetylacetonate to a depth of A of an inch and allowed to stand at ambient temperature for 1 week. At this time there was no apparent curing on the top surface, so as much as the liquid solution as possible was poured into a second aluminum dish. There was a layer of cured polythioether polymer on the bottom of the first dish where the iron compound was situated. This was stripped out and was found to have a thickness of mils and a shore A hardness of 49.

EXAMPLE Ill A glass plate was painted with a solution of mg. of ferric acetylacetonate in 3 ml. of acetone. The uncured portion of the polymer solution of example ll which was poured into a separate aluminum dish was poured over the painted glass plate and spread thereover with a glass rod. After 3 minutes the plate was washed with isopropanol and hot water removing all the uncured polymer except that in the ferric acetylacetonate treated area. On characterization there was found to be a 3 mil coating of a polythioether polymer on the glass plate.

EXAMPLE IV Ferric acetylacetonate was dusted onto one end of 1 inch wide strip of black plate steel. A solution comprising 30 g. of prepolymer A from example l, 5 g. Benzoflex 988," 2.3 g. Q43 and 0.5 g. of cyclohexanone oxime benzoate was added throughout both the ferric acetylacetonate treated end of the black plate steel and the untreated end. After 5 minutes an attempt was made to wipe off all of the liquid polyenepolythiol composition. All of the polyene-polythiol composition was removed from the untreated end of the steel but a 2 mil coating of the cured polythioether remained on the end of the black plate steel that had been treated with ferric acetylacetonate.

EXAMPLE V An iron pipe was coated with a solution comprising 30 g. of prepolymer A from example 1, 2.3 g. "Q-43" and 0.5 g. of cyclohexanone oxime benzoate. The coating was applied around the entire circumference of the pipe to a depth of approximately 5 mils. At the end of 5 minutes, a cured solidified hardened polythioether coating 5 mils thick) resulted on the iron pipe.

EXAMPLE VI 10 g. of prepolymer A from example I was admixed with l g. pentaerythritol tetrakis (B-mercaptopropionate) commercially available from Carlisle Chemical Co. under the trade name Q-43." The thus formed admixture was applied to commercially available bond paper by means of a Baker film applicator manufactured by Gardner Manufacturing Co., Bethesda, Md., to a depth of 2 ml. A solution of 3 g. of ferric ammonium sulfate in 200 ml. of water was prepared. The coated paper was immersed in the iron-containing solution for 5 seconds, removed, and allowed to cure in air. After 10 minutes a cured hardened polythioether coating resulted on the paper.

EXAMPLE VII 10 g. of prepolymer A from example I were admixed with l g. pentaerythritol tetrakis (Bmercaptopropionate) commercially available from Carlisle Chemical Co. under the trade name of Q-43 and 0.30 g. of cyclohexanone oxime benzoate. The thus-formed admixture was applied to the surface of two pieces of aluminum foil (1.5 mil thick) by means of a Baker film applicator to a depth of 1 mil. A solution of 3 g. of ferric ammonium sulfate in 200 ml. of water was prepared. The coated foils were immersed in the iron-containing solution for seconds, removed, and the coated surfaces on each foil were placed in contact with one another by hand pressing. After 2 minutes an attempt was made to pull the two aluminum foils apart which resulted in the foils tearing and substantially no injury to the hardened polythioether adhesive.

EXAMPLE Vlll reactive unsaturated carbon to carbon bonds per molecule, a polythiol containing at least two thiol groups per molecule, the total combined functionality of (a) the reactive unsaturated carbon to carbon bonds per molecule in the polyene and (b) the thiol groups per molecule in the polythiol being greater than four and the weight ratio of the polyene to the polythiol being 2 to 98:98 to 2 respectively and 0.1 to 5 percent by weight of the polyene-polythiol composition of an oxime ester (2) applying to said other substrate an iron-containing material as a prime coat (3) contacting the coated surfaces of the substrates and (4) allowing the curable polythioether adhesive composition to harden under ambient conditions.

2. The process according to claim 1 wherein the iron-containing material is added in a diluent. 

2. The process according to claim 1 wherein the iron-containing material is added in a diluent. 